Many valves have a rotatable flow control member positioned therein for controlling the flow of a fluid through the valve. The valve flow control member is rotated between open and closed positions to control the flow of fluid through the valve. In many cases, particularly for large valves used in industrial applications, the valve flow control member is rotated by a pneumatic cylinder actuator which is coupled to the valve shaft, which, in turn, is coupled to the valve flow control member. The pneumatic actuator typically includes a cylinder, a piston mounted in the cylinder, a piston rod attached to the piston and extending from the cylinder, and a structure for coupling the piston rod to the valve shaft to convert linear motion of the piston rod to rotational motion of the valve shaft. The valve flow control member is rotated by admitting and removing pressurized air from the cylinder, which moves the piston and the piston rod, to thereby rotate the valve shaft and flow control member.
In some cases, such as when maintenance of the valve is required, it is desirable to lock the valve flow control member in a desired position. This may be accomplished by preventing the pneumatic actuator from moving when air pressure is applied to the cylinder. A lockout device for the actuator must be able to withstand the fall force of the actuator without moving the valve.